It is well-known that the polyphenols of cocoa contribute significantly to the development of flavour in the fermented and roasted cocoa bean. Astringent and bitter flavors in cocoa have been traditionally associated with the presence of xanthine alkaloids and polyphenols in the cocoa beans. For this reason, various methods have been developed over the years to extract the cocoa polyphenols to verify their presence, to quantify their amounts, and to identify them. The cocoa polyphenols are primarily cocoa procyanidins. However, no extraction method has thus far been optimized to yield extracts high in cocoa procyanidins.
It is now known that the cocoa procyanidin oligomers show a clear relationship between structure and function, meaning that individual oligomers, or fractions containing several oligomers of a similar size, show specific biological functions which are not affected by other oligomers. Thus, it is important to ensure that the extraction procedure utilized not only results in the highest possible solubilization of the cocoa polyphenols, but that it is effective at extracting all the cocoa polyphenol oligomers present in the bean.
The extraction of cocoa beans using water or an organic solvent, or a mixture of water and an organic solvent has been used to remove the xanthine alkaloids (predominantly caffeine and theobromine) and other soluble constituents of the cocoa bean which impart a bitter, disagreeable flavor. Included among these bitter-tasting soluble constituents are the procyanidins.
U.S. Pat. No. 1,750,795 (issued to Defren in 1926) discloses a process for removing the “greater part of the soluble bitter constituents of the beans” by soaking the beans in water at 60° C. and then discarding the water and roasting the beans.
Hot water treatments have been used to remove the xanthines in order to provide stimulant-free cocoa beans. See U.S. Pat. No. 4,407,834 “Detheobromination of Cocoa” (issued to Chiovini et al., Jun. 28, 1983) and U.S. Pat. No. 4,755,391 “Removal of Methylxanthines from Cacao Materials” (issued to Bigalli et al., Jul. 5, 1988).
Cocoa extracts have been prepared by extracting cocoa solids, prepared from fermented, conventionally roasted cocoa beans or cocoa nibs, with water and/or alcohols. Osakabe et al. used ethanol, either absolute or aqueous at greater than 40% v/v with deionized water at ambient temperature to prepare a crude polyphenol extract. See JP 946-64717 “Food or Beverage Product for Preventing Gastric Ulcers” (Oct. 4, 1995).
Zieglader et al. used methanol to extract the polyphenols from cocoa beans at ambient temperature. See “Antioxidative Effects of Cocoa” (Rev. Choc. Confect. Bank, 8:3-6, 1983) which discloses the preparation of a methanol extract. The extract contained “monomer tannin precursors (catechins, anthocyanidins and their soluble condensates)” and that is used as an additive for oil to preserve it from oxidation. Griffiths et al. used methanol extracts, again obtained at ambient temperatures, to obtain polyphenol extracts from ripe cocoa nibs which were used to study the characterization of plant polyphenols in cocoa and other plants. See “A Comparative Study of the Seed Polyphenols of the Genus Theobroma”, (Biochemical J. 74:362-365, 1960). Rigaud et al. made an extract from lyophilized cocoa beans and grape seeds and noted that the use of methanol as a solvent precluded the presence of the higher oligomers. See “Normal-Phase High-Performance Liquid Chromatographic Separation of Procyanidins from Cacao Beans and Grape Seeds (J. Chromatography 654:255-60, 1993). Jalal & Collin prepared extracts from different parts of the cocoa plant in order to analyze the polyphenols present in each part of the plant. The extraction was carried out using 70% cold methanol, followed by ethyl acetate. See Polyphenols of Mature Plant, Seedling and Tissue Cultures of Theobroma Cacao” (Phytochemistry, 16:1377-1380, 1977).
Acetone/water has also been used for cocoa bean extractions. Clapperton et al. report the extraction of defatted cocoa powder made from fermented cocoa bens using cold 70% acetone. See “Polyphenols and Cocoa Flavor, Groupe Polyphenols,” (XVIth Intern. Conf., Lisbon, Portugal, Jul. 13-16, 1992). Rigaud combines a first extraction with ethanol with a second extraction using a 60% acetone/water mixture. See “Normal-Phase High-Performance Liquid Chromatographic Separation of Procyanidins from Cacao Beans and Grape Seeds” (J. Chromatography 654:255-60, 1993).
Traditionally, cocoa beans are treated and processed in such a way as to minimize the bitter taste which the polyphenols impart to the beans, and this results in a reduction of the polyphenol content of the bean. The two ways in which the polyphenol content is significantly reduced are fermentation of cocoa beans in their husks and roasting the fermented cocoa beans in order to crack their husks and aid in the de-hulling process. Zieglader et al. report a loss of antioxidant activities in extracts from cocoa beans which are fermented compared to extracts from unfermented beans and correlate this reduction in antioxidant potential with a reduced amount of polyphenols in the extracts of fermented beans. All the previously discussed extraction methods were carried out using fermented beans, and in many cases the beans were also roasted. Therefore, the procyanidin yields are much lower than those found in extracts from unfermented beans.
It has been a common practice to follow an initial solvent extraction step with an ethyl acetate extraction step. See Forsyth & Roberts, “Cacao Polyphenolic Substances: 3. The Structure of Cacao Leucocyanidin 1” Biochem. J. 74 374-378, 1960; Thompson et al., “Plant Procyanidins. Part 1. Introduction: the Isolation, Structure and Distribution in Nature of Plant Procyanidins”, J. Chem. Soc. Perkin 1, Vol. 11, 1387-99, 1972; Jalal & Colllins, “Polyphenols of Mature Plant, Seedling and Tissue Cultures of Theobroma Cacao”, Phytochemistry, 16:1377-1380, 1977; Porter et al. “Flavans and Proanthocyanidins” Chapter Two in “The Flavanoids”, Ed., J.B. Harborne, Chapman and Hall Ltd., London, 1988; and U.S. Pat. No. 5,554,645 (issued Oct. 3, 1994 to Romanczyk et al). This has the effect of producing an extract which contains the monomers and lower oligomers and none, or very little, of the higher oligomers. See Lea A. “The Phenolics of Ciders: Oligomeric and Polymeric Procyanidins”, J. Sci. Fd. Agric. 29 471-477, 1978.
Whether or not the cocoa beans are defatted prior to extraction has an impact upon the yield of polyphenols extracted. If the beans are not defatted, the fat in the beans interferes with the solubilizing activity of the solvent, and the polyphenol yields are considerably reduced (Lazarus et al. “Flavonoids and Other Polyphenols” in Methods in Enzymology series. Edited by Lester Packer, Academic Press, New York, in press).
Cocoa extracts have been prepared from cocoa solids prepared from unfermented or fermented sun dried cocoa beans. The beans were ground, defatted and extracted. A 70% acetone/30% deionized water mixture was used, followed by a 70% methanol extraction and two chloroform extractions. Then follows an extraction with ethyl acetate, the addition of water, and the removal of the ethyl acetate. Alternatively, the beans were extracted with 70% acetone. In both cases the extractions were carried out at room temperature and the aqueous extracts were freeze-dried. See U.S. Pat. No. 5,554,645 (issued Oct. 3, 1994 to L. Romanczyk et al.).
Furthermore, cocoa extracts can be prepared from partially defatted cocoa solids that are prepared from cocoa beans which have not been roasted. The resulting cocoa solids, whether prepared from fermented, underfermented, or unfermented cocoa nibs, have a higher cocoa polyphenol content, i.e., cocoa procyanidin content, than cocoa solids prepared from conventionally roasted cocoa beans or cocoa nibs. See U.S. Pat. No. 6,015,913 (issued Jan. 18, 2000 to K. S. Kealey et al.).
Defatted, freeze-dried, unfermented cocoa beans contain about 2% xanthine alkaloids, and traditionally processed beans contain larger amounts. Theobromine is a degradation product of caffeine, and both are well-known stimulants of the nervous system. Excessive xanthine alkaloid intake is not thought to be beneficial. Hence, in some cases, it may be desirable to prepare cocoa extracts free of the xanthine alkaloids.
Thus, there is a need for an improved process to extract cocoa procyanidins from cocoa solids, and, in some cases, to decaffeinate and detheobrominate the cocoa extracts.